1. Field of the Invention
This invention relates to a method of depositing a metal on a surface and more particularly, to a method of selectively depositing a metal on a surface of an electrically non-conducting substrate.
2. Discussion of the Prior Art
There is a growing need in various devices and circuit applications for an inexpensive process which will produce adherent conducting circuit patterns on a non-conductor surface. Most of the processes used for metallic pattern generation involve a photographic step. Pattern resolution may be good but most methods are often slow, involving many process steps, and are relatively expensive.
A conventional method of producing macro circuit patterns employs a copper-clad insulator board coated with a photoresist material which is photoexposed and chemically processed to selectively remove copper, leaving a desired circuit pattern. This method is effective but wasteful of copper and chemicals. The high cost of this method has encouraged research and development toward new techniques for metallic pattern generation on a non-conductor surface.
An electroless metal-deposition process is especially attractive for metallic pattern generation since one only needs to produce a pattern of a suitable catalyst on a substrate and metal desposition will occur only on that pattern. One selective electroless metal deposition, described in U.S. Pat. No. 3,632,435, prepares a substrate surface whereby the surface has divergent surface characteristics with respect to the retention of (1) a colloidal stannous salt, or (2) a colloidal noble metal applied from a bath containing a stannous salt and a noble metal salt. The divergent surface characteristics are obtained by rendering a selected area smooth as compared to another area (rough) or vice-versa. The relatively rougher area will retain the colloidal material upon treatment with a reactive stripper or destabilizing media whereas the smoother surface will not. The stripper materials include solutions of strong electrolytes or organic compounds which react with the colloidal tin or noble metal species. The use of roughening and/or smoothing expedients as well as the use of reactive strippers involves several process steps which lengthens the process and makes it relatively expensive.
A method for selective metal deposition utilizing an electroless metal-deposition technique without the use of roughening and/or smoothing expedients and/or reactive stripping or destabilizing expedients is desired and needed.